i2s_channel_register_event_callback() function

- ESP_OK Set event callbacks successfully - ESP_ERR_INVALID_ARG Set event callbacks failed because of invalid argument - ESP_ERR_INVALID_STATE Set event callbacks failed because the current channel state is not REGISTERED or READY

Only allowed to be called when the channel state is REGISTERED / READY, (i.e., before channel starts) User can deregister a previously registered callback by calling this function and setting the callback member in the `callbacks` structure to NULL. When CONFIG_I2S_ISR_IRAM_SAFE is enabled, the callback itself and functions called by it should be placed in IRAM. The variables used in the function should be in the SRAM as well. The `user_data` should also reside in SRAM or internal RAM as well.